Method of making vacuum type electric incandescent lamps



Aug. 19,1969 ye. FRIDRICH 9 METHODOF MAKING VACUUM TYPE ELECTRIC INCANDESCENT LAMPS Filed Jan. 4, 1968 lnven lfow': ELmeT- GFTich-ich United States Patent 3,462,209 METHOD OF MAKING VACUUM TYPE ELECTRIC INCANDESCENT LAMPS Elmer G. Fridrich, Munson Township, Geauga County,

Ohio, assignor to General Electric Company, a corporation of New York Filed Jan. 4, 1968, Ser. No. 695,698 Int. Cl. H01j 9/18 US. Cl. 316-19 4 Claims ABSTRACT OF THE DISCLOSURE An electric incandescent lamp of the vacuum type is manufactured by positioning the filament thereof in sealing relation within an envelope of fused quartz, flushing the interior of the envelope with helium gas to drive out the contained atmosphere therefrom and, during the continuance of the gas flushing operation, sealing the filament into the envelope, and then heating the sealed envelope to an elevated temperature for a period of time sufficent to diffuse the helium gas therein outwardly through the wall of the envelope to thereby create substantially a vacuum therewithin.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method of manufacturing electric lamps or similar devices comprising a bulb or envelope having an electric energy translation element or filament sealed therein. More particularly, the invention relates to the manufacture of electric incadescent lamps of the so-called miniature type having sealed cnclosure envelopes or tubes the interior space of which is substantially gas free.

Description of the prior art Electronic systems are continually being developed having extremely compact circuits, to allow complex circuits to be provided in a small space and with low power requirements. Many of these circuits are monitored by electric incandescent indicator lamps. As the circuits are miniaturized, so must the lamps, to provide a compact package which may, by visual observation of the lighted or unlighted condition of the indicator lamp, be checked for reliability and for its operability.

Miniature size incandescent lamps such as, for example, the microminiature incandescent lamps commonly employed in compact circuit applications such as referred to above, are customarily formed with a vacuum in the lamp envelope, it being undesirable to employ a conventional type lamp gas filling in such miniature size lamps because of the significant cooling effect which the gas filling would normally have on the filament with consequent loss of light output therefrom. The customary procedure employed heretofore to produce the vacuum within the lamp envelope has been to vacuum exhaust the envelope through an exhaust tube provided thereon, the exhaust tube being tipped off after the evacuation of the envelope is completed. The effectiveness, however, of this vacuum exhaust method of creating the vacuum in the lamp envelope decreases and becomes quite a problem as the lamp envelope and exhaust tube diameters are decreased.

SUMMARY OF THE INVENTION It is an object of the invention, therefore, to provide a novel method of making a vacuum type electric incandescent lamp or similar device which does not involve the vacuum exhaust thereof.

Another object of my invention is to provide a method of making vacuum type electric incandescent lamps or similar devices which is particularly suited for the manufacture of microminiature size devices of such type.

Still another object of the invention is to provide a novel method of producing a vacuum type electric incandescent lamp or similar device of double-ended character.v

Briefly stated, in accordance with one aspect of the invention, the manufacture of an electric incandescent lamp or similar device of the vacuum type is accomplished by employing, for the envelope of the lamp, one made of fused quartz, and then, with the filament assembly of the contained atmosphere therefrom and heating the enlope, flushing the envelope with helium gas to expel all the contained atmosphere therefrom and heating the envelope during the continuance of the gas flushing thereof to release the occluded gases therein, next sealing the filament assembly into the envelope, while continuing the flushing thereof with helium gas, to thereby hermetically seal off the envelope from the surrounding atmosphere, and the heating the hermetically sealed envelope to an elevated temperature to diffuse the helium gas present therein outwardly through the wall of the envelope at an accelerated rate and maintaining the envelope at such elevated temperature until substantially a vacuum is created therein.

Further features and advantages of the invention will appear from the following detailed description of species thereof and from the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing,

FIGS. 1 and 2 illustrate the successive steps involved in the manufacture of an electric incandescent lamp according to the invention;

FIG. 3 is a side elevation of the finished lamp; and

FIGS. 4 and 5 illustrate the successive steps involved in the manufacture, according to a modification of the invention, of a single-ended type of electric incandescent lamp.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For the purpose of convenience and not by way of limitation, the invention is described hereinafter with particular reference to an electric incandescent lamp of miniature size. It should be understood, however, that this description is merely exemplary of the facets in which the invention can be applied and is not limiting to the scope of either the invention or the appended claims.

Referring to FIG. 1, in the manufacture of one form of vacuum type electric incandescent lamps by the method according to the invention, there is employed, as the member from which the lamp envelope 1 (FIG. 3) is fabricated, a length of tubing 2 of a light-transmissive vitreous material which is permeable to helium gas. For such purpose, the vitreous tube 2 is composed of essentially fused silica, such as fused quartz or a material known as 96% silica glass such as that commercially known as Vycor. Because of its high permeability to helium, however, quartz is preferred as the material for the tube 2, hereinafter generically referred to as a quartz tube or envelope. Since the invention, although not limited to the manufacture of any particular size of lamp nevertheless is especially suited to the manufacture of lamps of less than 0.5 cc. bulb volume, and particulary lamps of the so-called microminiature type having extremely small envelopes, the quartz tube 2 therefore may be as small as that commonly referred to as of capillary size and having inside diameters as little as 0.5 mm. or thereabouts.

The fabrication of a lamp in accordance with the invention is initiated by first inserting completely into the quartztube 2 an electricalenerg-y.translation-element or,

filament assembly 3 of the axially extending type comprising a light-producing linear translation element or filament body portion 4 of tungsten wire fromv the opposite ends of which extend lead-in conductor seal portions 5, 5' terminating in outer conductor portions 6, 6'. The lightproducing body portion 4 of the filament assembly 3 may be of coiled form as shown, -or it may be of straight wire form, depending upon the design wattage of the lamp. The lead-in conductor seal portions 5, 5' of the filament assembly 3 extend liriearly'of the filament body portion 4 and they may, as shown, comprise simply an extension or continuation of the tungsten wire of which the filament .of the helium-gas through the quartz tube, the latter is suitably heated and softened at a region adjacent the outlet end 9 of the quartz tube and outwardly beyond the corresponding end of hte filament assembly 3 therein, as by directing oxyhydrogen gas fires 11 against such region of'the quartz tube from gas burners 12 disposed thereadjacent, to cause the quartz tube to collapse and thereby completely close or seal off the quartz tube 2 at the region A thereof, as indicated at 13 in FIG. 2. If desired, the softened region of the quartz tube 2 may be pinched shut at the region A to form the seal 13 by the closure thereagainst of pinching jaws (not shown) inthe manner cusg tomary in the lamp art for making pinch seals of metal body portion4 is formed, providing the wire diameter thereof is no greater than around 4 mils or so, since tungsten wire up to such wire diameters can be effectively sealed directly into quartz to form a hermetic seal therewith. The outer conductor portions 6, 6' of the filament assembly 3 may also be constituted of wire, e.g., as further continuations of the tungsten wire' filament 4 andseal portions 5, 5' of the filament assembly 3, and they may be formed with S-shaped or helical configurations, as shown at 7, 7', which are adapted'to snugly fit across the inside diameter of the quartz tube 2 in order to thereby support and locate the filament assembly 3 in approximately centered position within the quartz tube 2 along the axis thereof, prior to and during the sealing-in of the filament assembly 3 into the quartz tube. Of course, any other suitable means may be employed for holding the filament assembly 3 in such centered sealing-in position axially of the quartz tube 2 during the sealing-in operation, so long as the means employed for such purpose does not obstruct the free passage through the quartz tube of a flushing gas therefor. For example, the outer conductor portions 6, 6' may be constituted of ribbon-like tabs of molybdenum spot-welded to the seal portions 5, 5' of the filament assembly 3 and sungly fitting within the quartz tube 2 across the diameter thereof. As shown in FIG. 1, the quartz tube 2 is sufficiently longer than the overall length of the filament assembly 3 to permit the quartz tube to be sealed or closed off at points outwardly beyond the respective ends of the filament assembly 3 when the latter is located in sealing position therein, i.e., in more or less centered position lengthwise of the quartz tube 2.

With the filament assembly 3 thus inserted and supported in sealing position within the quartz tube 2, the interior of the said tube is then flushed with helium gas by introducing the gas into one open end thereof, e.g., into an inlet end 8 of the quartz tube as indicated by the arrow in FIG. 1, and allowing the helium gas to escape from the other or outlet end 9 of the quartz tube, in order to there by expel the contained atmosphere from within the tube and replace it with the inert helium gas. For the purposes of the invention, the fiow of the helium gas through the quartz tube 2 may be produced by discharging the helium gas into the quartz tube from one end of a hollow flushing needle or snorkel tube 10 inserted a short distance into the inlet end 8 of the quartz tube 2 and connected at its other end to a valved supply of helium gas at a pressure slightly above atmospheric and just high enough to produce a gentle stream or flow of the helium gas through the quartz tube as well as back along the outer side of the snorkel tube 10 and out the inlet end 8 of the quartz tube so to prevent any back flow of the surrounding atmosphere thereinto. During the continuance of the helium gas flushing operation, the quartz tube 2. is heated' or baked at an elevated temperature, preferably just below its softening point, to thereby drive out the occluded gases there from as well as from the filament assembly 3 positioned therein, the occluded gases thus released into the quartz tube then also being flushed out of the tube by the helium flushing gas passing therethrough. I

Upon passage of a sufficienttime to assure the complete removal of the contained atmosphere and occluded gases from within the quartz tube 2 by the heating and helium gas flushing thereof, and while continuing the flow conductors into quartz or glass lamp envelopes.

Following the completion of the seal 13 at the region A of the quartz tube 2, and while continuing the aforementioned flushing thereof with helium gas directed into the tube from the flushing nozzle 10 inserted therein, the quartz tube 2 is then completely sealed off at a second region B thereof (FIG. 2), surrounding that seal portion 5 of the filament assembly 3 located next adjacent the first seal 13 formed in the quartz tube, to thereby hermetically seal the said seal portion 5 of the filament assembly into the quartz tube 2, as indicated at 14 in dotted lines in FIG. 2. The sealing of the quartz tube 2 around the seal portion 5 of the filament assembly 3 to form the seal 14 may be effected in a manner similar to that employed to form the seal 13, i.e., by suitably heating and softening the quartz tube 2 at the region B thereof, as by directing gas fires 15 thereagainst from gas burners 16 disposed adjacent the quartz tube, to cause the quartz tube to collapse around and embed the seal portion 5 of the filament assembly 3. Preferably, however, the softened quartz tube 2 is firmly pinched or pressed down upon the seal portion 5 of the filament assembly 3, in order to flatten and assure a tight hermetic seal of the quartz tube around the seal portion 5 of the filament assembly, by the closure of pinching jaws (not shown) against the softened region B of the quartz tube, in the manner customary in the lamp art for making conventional type pinch seals.

After completion of the seal 14 in the quartz tube 2 and while continuing the flow of helium gas thereinto from the flushing tube 10 inserted therein, a third hermetic seal 17 similar to the seal 14 is formed in the quartz tube 2 at the region C thereof (FIG. 2) surrounding the other seal portion 5 of the filament assembly 3 to thereby hermetically seal the quartz tube 2 around the lead-in conductor seal portion 5' of the filament assembly 3. The forming of this third hermetic seal 17 in the quartz tube at the same time serves to complete the formation thereof into an envelope portion 1 (FIG. 3) hermetically enclosing the filament body portion 4 of the filament assembly 3. The lead-in conductor seal 17 may be formed in the same manner as the other lead-in conductor seal 14, by suitably heating and softening the quartz tube 2 at the region C thereof, as by directing oxyhydrogen gas fires thereagainst, to cause the softened quartz to collapse down onto and embed the lead-in conductor seal portion 5', and preferably also compressing the softened portion of the quartz tube between pinching jaws (not shown) to form a flattened seal 17 similar to the seal 14.

Following the completion of the lead-in conductor seal 17, and while the flow of helium gas into the quartz tube 2 is continued from the flushing tube 10 inserted thereinto, a fourth hermetic seal 18 similar to the seal 13 is then formed in the quartz tube 2, at a region D thereof (FIG. 2) adjacent its inlet end 8 and outwardly beyond the corresponding outer conductor end portion 6' of the filament assembly 3, to thereby completely seal the filament assembly 3 hermetically within the quarty tube 2. The hermetic seal 18 may be formed in the same manner as the seal 13, by heating and softening the quartz tube 2 at the region D thereof, as 'by directing oxyhydrogen gas fires thereagainst, to cause the softened quartz tube to collapse and seal together so as to completely close or seal it off. If desired, while the quartz at the region D is still in a softened condition, it may be pinched shut by the closure thereagainst of pinching jaws (not shown) to thereby form a pinch-type seal 18.

With the entire filament assembly 3 thus completely sealed hermetically within the quartz tube 2 between the two seals 13, 18 therein, the helium gas present within the envelope portion 1 of the quartz tube 2 is then diffused outwardly through the wall of the tube to thereby create a vacuum therein. To this end the quartz tube 2 is, in accordance with the invention, raised to an elevated temperature, as by heating or baking it in an oven to a temperature of several hundred degrees C., e.g., around 800 C. or thereabouts, to accelerate the rate of diffusion of the helium gas outwardly through the wall of the quartz tube appreciably over that which occurs at normal room temperature. The heating or baking of the quartz tube is continued until the pressure of the helium gas remaining within the hermetically sealed envelope portion 1 thereof approximates, or nearly approximates, the partial pressure of the helium present in the air or other surrounding atmosphere. To reduce the amount of helium remaining in the sealed quartz tube 2 to less than that present in air, the quartz tube in such case is baked in a surrounding atmosphere of nitrogen or other inert gas to which the quartz tube is impermeable. The time duration of the baking of the sealed quartz tube 2 necessary to create substantially a vacuum in the envelope portion 1 thereof will, of course, depend on various factors such as the baking temperature employed, the wall thickness and diameters of the tubular envelope portion 1 as Well as the composition thereof, and the degree of vacuum desired in the finished lamp. As an example, however, for a lamp with a tubular envelope 1 of fused quartz of approximately 1 millimeter outside diameter and .6 millimeter inside diameter, a baking of the envelope 1 in air for a time of around 48 hours at a temperature of 800 C. or so will operate to reduce the helium pressure inside the lamp envelope 1 to virtually the same as the partial pressure of the helium in the air outside the envelope. Since the outer conductor portions 6, 6' of the filament assembly 3 are hermetically sealed into the quartz tube 2 and thus isolated from the surrounding atmosphere, they are therefore kept from being oxidized during the baking operation such as would otherwise cause the burnout of these outer conductor portions 6, 6' when made of fine wire, in the case where the baking operation is carried out in air. Without such hermetic sealing of the outer conductor portions 6, 6' into the quartz tube 2, it would be necessary to carry out the baking operation in a nitrogen or other inert gas atmosphere in order to thereby avoid the oxidation and burn-out of the outer conductor portions 6, 6'.

After the baking of the sealed quartz tube 2 to establish substantially a vacuum in the lamp envelope portion 1 thereof is completed, the end portions of the quartz tube 2 outwardly beyond the outer ends of the seals 14 and 17 are then suitably removed, as by cutting them off with a diamond or other abrasive cutting Wheel, to thereby expose the outer conductor portions 6, 6' and complete the fabrication of the lamp 1.

The lamp manufacturing process according to the invention may be advantageously employed to form a single-ended type of lamp 20 such as shown in FIG. 5, as well as a double-ended lamp as shown in FIG. 3. T0 manufacture such a single-ended lamp 20, a preformed filament mount or assembly 21 (FIG. 4) is supported in sealing position within a tubular bulb or envelope 22 having a closed end and constituted of the same quartz type material described hereinbefore in connection with the manufacture of the double-ended lamp illustrated in FIGS. 1-3. The filament mount or assembly 21 is comprised of a tungsten wire filament 23 of any suitable form, e.g., of straight or coiled form, connected at its 0pposite ends to a pair of generally parallel extending tungsten lead-in conductors or wires 24 which may comprise an extension or continuation of the tungsten wire of which the filament 23 is formed, as described in connection with FIGS. 1-3. As shown, the filament mount or assembly 21 is supported in upright position on a suitable mount holder pin 25 having openings 26 in its upper end for snugly receiving the lower or outer ends of the lead-in conductors 24 to thereby support the filament assembly 21 in place on the holder pin 25. The mount holder pin 25 also has a vertically extending bore or passageway 27 therein which is located between the two conductor-receiving openings 26 and terminates at its upper end in a gas flushing orifice 28 in the upper end of the mount pin 25. At its lower end, the passageway 27 is suitably connected to a valved supply of helium gas such as described hereinbefore. The quartz envelope 22 is supported in a suitable envelope holder (not shown) with its open end 29 facing downwardly and spaced a very slight distance above the upper end of the mount pin 25 so as to afford only a very restricted passageway therebetween.

With the envelope 22 and filament assembly 21 thus supported in sealing relation to each other as described above, the interior of the quartz envelope 22 is then flushed with helium gas by directing the gas thereinto from the flushing orifice 28 at the upper end of the bore 27 in the mount holder pin 25, and allowing the helium gas to escape from the envelope 22 through the restricted space between the lower end of the envelope and the upper end of the mount pin 25, the rates of flow of the helium gas into the envelope 22 and out the space between its lower end and the mount pin 25 being just sufiicient to prevent any back flow of the surrounding atmosphere into the envelope 22 through the restricted space between the envelope and the mount pin 25. During the continuance of the helium gas flushing operation, the envelope 22 is heated or baked at an elevated temperature, preferably just below its softening temperature, to thereby drive out the occluded gases therefrom as well as from the filament assembly 21 positioned therein, the occluded gases thus released into the envelope 22 then also being flushed out of the envelope by the helium flushing gas introduced thereinto.

After the passage of sufficient time to assure the complete removal of the ambient atmosphere and occluded gases from within the quartz envelope 22 by the heating and helium gas flushing thereof, and while continuing the flow of the helium gas into the envelope, the lower end region of the envelope 22 is then suitably heated and softened, as by directing oxyhydrogen gas fires 30 thereagainst from gas burners 31 disposed thereadjacent, and the softened lower end region of the quartz envelope 22 then pinched or pressed down onto the lead in conductors 24, as by the closure thereagainst of pinching jaws 33 (FIG. 5) against the sofened lower end region of the quartz envelope 22, in the manner customary in the lamp art for making conventional type pinch seals, to thereby flatten and form a tight hermetic seal 32 of the quartz envelope around the said conductors. During the heating and sealing operation, the helium gas which is present within the envelope 22 as well as within the openings 26 in the mount pin 25, acts to prevent the oxidation of the filament 23 and lead-in conductors 24 of the filament assembly 21.

Instead of introducing the helium flushing gas into the envelope 22 from an orifice 28 in the upper end of the mount pin 25, a retractable flushing tube (not shown) may be employed for such purpose, similar to the flushing tube 10 in FIGS 1 and 2, the flushing tube in such case being vertically movable within the mount pin 25 for insertion a short distance into the open lower end of the envelope 22 during the gas flushing of the envelope and ensuing heating and softening thereof, and being subsequently withdrawn from inside the envelope 22 just prior to the pinching of the softened lower end of the envelope to form the seal 32, as disclosed in Patent No. 2,900,771, Levand.

After the completion of the seal 32 of the quartz envelope 22 around the lead-in conductors 24, the sealed envelope 22 is then heated and baked at an elevated temperature, in the same manner as described above in connection with FIGS. 13, to cause the diffusion of the helium gas present within the envelope 22 outwardly through the walls thereof to the outside at an accelerated rate. As before, the heating and baking of the sealed envelope 22 is continued until the pressure of the helium gas remaining within the envelope approximates, or nearly approximates, the partial pressure of helium present in atmospheric air, whereby substantially a vacuum is created within the envelope 22. A vacuum type lamp 20 is thereby produced which effectively retains its vacuum throughout the operating life of the lamp. Since the outer end portions 34 (FIG. 4) of the lamp lead-in conductors 24, which serve as the wire terminals for the finished lamp, are exposed to the heat of the lamp baking operation, it is therefore necessary to carry out this lamp baking operation in an inert atmosphere, as in a conventional type nitrogen furnace for example, in order to thereby prevent the oxidation and burning out of these exposed outer end portions 34 of the lead-in conductors 24. However, to avoid the necessity of carrying out the baking operation in a nitrogen or other inert gas atmosphere, the envelope 22 may be extended beyond the outer ends 34 of the lead-in conductors 24 and hermetically sealed off at a region outwardly therebeyond so as to completely enclose and seal off the said outer end portions 34 of the lead-in conductors from the surrounding atmosphere. On completion of the lamp baking operation, the extended potrion of the lamp envelopes 22 is then suitably removed, as by cutting it off with an abrasive cutting Wheel, to thereby expose the outer ends 34 of the lead-in conductors 24.

From the above description of the invention, it will be apparent that I have devised a novel lamp-making method that enables the manufacture of vacuum type electric incandescent lamps without the need for the vacuumexhausting thereof. As a result, vacuum type electric lamps and similar devices of extremely small size, such as the so-called microminiature type lamps having envelopes as small as capillary tube size, and having the required high degree of vacuum therein, can be produced with much less difficulty than in the case heretofore where vacuum exhausting of the lamp is required.

Although preferred embodiments of my invention have been disclosed, it will be understood that the invention is not to be limited to the specific procedures described, but that they may be widely modified within the spirit and scope of my invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making an electric incandescent lamp comprising the steps of positioning a filament assembly in sealing relation with an envelope of fused quartz having an open end, flushing the interior of said envelope through said open end with helium gas and, during the continuance of said helium gas flushing of the envelope, heating the said envelope to an elevated temperature to drive out the occluded gases therefrom, sealing said filament assembly into the said envelope while continuing the said flushing thereof with helium gas, and then heating the sealed envelope to an elevated temperature to diifusse the helium gas present therein outwardly through the wall of said envelope to the outside thereof to thereby create substantially a vacuum therein.

2. The method of making an electric incandescent lamp as specified in claim 1 wherein the said heating of the sealed envelope is carried out in air and at an elevated temperature of several hundred degrees C. for a period of time suflicient to reduce the pressure of the helium gas remaining in the envelope to approximately the partial pressure of helium in the surrounding air.

3. The method of making an electric incandescent lamp as specified in claim 1 wherein the said heating of the sealed envelope is carried out in a surrounding atmosphere of nitrogen and at an elevated temperature of several hundred degrees C. for a period of time sufficient to reduce the pressure of the helium gas remaining in the envelope to a level below the partial pressure of helium in air.

4. The method of making a double-ended electric incandescent lamp provided with a filament assembly comprised of a linear light-producing body portion and leadin conductors extending endwise therefrom and including seal portions and outer conductor portions, sad method comprising the steps of positioning said filament assembly lengthwise within a tubular envelope of fused quartz having open ends,, flushing the interior of said tubular envelope with helium gas by introducing the helium gas into one of its open ends and out its other open end and, during the continuance of said helium gas flushing of the envelope, heating the said envelope to an elevated temperature to drive out the occluded gases therefrom, progressively heating and hermetically sealing off to said tubular envelope, While continuing the said flushing thereof with helium gas, firstly at a region of the envelope adjacent its said other end and outwardly beyond the corresponding end of the filament assembly positioned therein, secondly at the region of that seal portion of the filament assembly nearest the said other end of the envelope, thirdly at the region of the other seal portion of the filament assembly, and lastly at a region adjacent the said one end of the envelope and outwardly beyond the corresponding end of the filament assembly positioned therein, heating the sealed tubular envelope to an elevated temperature to diffuse the helium gas present therein outwardly through the wall of said envelope to the outside thereof to thereby create substantially a vacuum therein, and then removing the portions of said envelope outwardly of the said seal portions of said leadin conductors to thereby expose the said outer conductor portions thereof.

References Cited UNITED STATES PATENTS 3,211,511 10/1965 Levand 31619 3,301,623 1/1967 Pereziosi 3l62l RICHARDH. EANES, JR., Primary Examiner 

